• Authors:
    • Field,C. B.
    • Lobell, D. B.
  • Source: Environmental Research Letters
  • Volume: 2
  • Issue: 1
  • Year: 2007
  • Summary: Changes in the global production of major crops are important drivers of food prices, food security and land use decisions. Average global yields for these commodities are determined by the performance of crops in millions of fields distributed across a range of management, soil and climate regimes. Despite the complexity of global food supply, here we show that simple measures of growing season temperatures and precipitation - spatial averages based on the locations of each crop - explain similar to 30% or more of year-to-year variations in global average yields for the world's six most widely grown crops. For wheat, maize and barley, there is a clearly negative response of global yields to increased temperatures. Based on these sensitivities and observed climate trends, we estimate that warming since 1981 has resulted in annual combined losses of these three crops representing roughly 40 Mt or $5 billion per year, as of 2002. While these impacts are small relative to the technological yield gains over the same period, the results demonstrate already occurring negative impacts of climate trends on crop yields at the global scale.
  • Authors:
    • Burgener, P. A.
    • Felter, D. G.
    • Nielsen, D. C.
    • Lyon, D. J.
  • Source: Agronomy Journal
  • Volume: 99
  • Issue: 2
  • Year: 2007
  • Summary: Winter wheat (Triticum aestivum L.) is the foundation of dryland cropping systems in the Central Great Plains. The objective of this study was to quantify the effects of four short-season spring-planted crops used to replace summer fallow on the subsequent winter wheat crop. Wheat was seeded into four crop stubbles [spring triticale (xTriticosecale Wittmack), dry pea (Pisum sativum L.), foxtail millet (Setaria italica L. Beauv.), and proso millet (Panicum miliaceum L.)] at sites near Akron, CO, and Sidney, NE, in the fall of 2004 and 2005. These summer fallow replacement crops were planted into silt loam soils at three different soil water levels at planting (low, medium, and high). Winter wheat water use was 3.6 cm greater, and grain yield was 662 kg ha-1 greater in the high water treatment compared with the low water treatment averaged across all sites and years. Winter wheat used an average of 4.3 cm more water following early planted summer crops (triticale and dry pea) than after late planted summer crops (foxtail and proso millet), but this increased water use did not consistently translate into increased grain yield as a result of terminal drought at Sidney in 2006. The high water treatment always had a positive net return. The high cost of pea seed ($3.30 kg-1, USD) strongly reduced profitability. The flexible summer fallow cropping system appears to be most applicable when using short-duration summer annual forage crops such as triticale and foxtail millet.
  • Authors:
    • Qu, A.
    • Rhinhart, K.
    • Petrie, S.
    • Machado, S.
  • Source: Soil & Tillage Research
  • Volume: 94
  • Issue: 2
  • Year: 2007
  • Summary: Conventional tillage winter wheat (Triticum aestivum) (WW)-summer fallow reduces soil productivity and increases soil erosion. Conservation tillage management, together with intensive cropping may have the potential to reverse these sustainability concerns. The objective of this study was to determine the effects of conventional tillage (CT) and no-tillage (NT) systems on grain yield of long-term annual cropping of monoculture WW, spring wheat (SW), and spring barley (Hordeum vulgare) (SB) grown with or without fertilizer, in the Pacific Northwest region of the USA. In unfertilized crops, grain yield of WW, SW, and SB was 15%, 25%, and 50% higher, respectively, in CT than in NT plots, an indication of the involvement of yield limiting factors under the NT cropping system. When fertilized, there were no significant differences in grain yield of WW. Yields of SW and SB, however, remained 21% and 15% higher, respectively, in CT than in NT, an indication that factors other than fertility were involved. These results suggest that in order for NT management to be widely adopted by area growers, the yield-limiting factors need to be addressed.
  • Authors:
    • Harben, R.
    • Beyer, J.
    • Dusault, A.
    • Fry, R.
    • Shrestha, A.
    • Klonsky, K. M.
    • Mitchell, J. P.
  • Source: Australian Journal of Experimental Agriculture
  • Volume: 47
  • Issue: 12
  • Year: 2007
  • Summary: While there have been several similarities between the development of cropping systems in Australia and California ( including climate, the need for irrigation and very diverse, highly specialised crop rotations), the historical patterns of conservation tillage development in the two regions have been quite different. Current estimates indicate that conservation tillage ( CT) practices are used on less than 2% of annual crop acreage in California's Central Valley. Tillage management systems have changed relatively little since irrigation and cropping intensification began throughout this region, more than 60 years ago. The University of California ( UC) and United States Department of Agriculture ( USDA) Natural Resource Conservation Service ( NRCS) CT Workgroup is a diverse group of UC, NRCS, farmer, private sector, environmental group and other public agency people. It has provided wide- ranging services aimed at developing information on reduced tillage alternatives for California's production valleys. In a short span of 7 years, the CT Workgroup has grown to over 1000 members and has conducted over 60 demonstration evaluations of CT systems. While CT is still quite new in California, a growing number of farmers has become increasingly interested in it, for both economic and environmental reasons. They are now pursuing a wide range of activities and approaches aimed at developing sustainable CT systems. As successful CT systems continue to be demonstrated, the rate of adoption is expected to increase.
  • Authors:
    • Paustian, K.
    • Capalbo, S.
    • Antle, J.
    • Gerow, K.
    • Mooney, S.
  • Source: Climatic Change
  • Volume: 80
  • Issue: 1-2
  • Year: 2007
  • Summary: Several studies have suggested that geostatistical techniques could be employed to reduce overall transactions costs associated with contracting for soil C credits by increasing the efficacy of sampling protocols used to measure C-credits. In this paper, we show how information about the range of spatial autocorrelation can be used in a measurement scheme to reduce the size of the confidence intervals that bound estimates of the mean number of C-credits generated per hectare. A tighter confidence interval around the mean number of C-credits sequestered could increase producer payments for each hectare enrolled in a contract to supply C-credits. An empirical application to dry land cropping systems in three regions of Montana shows that information about the spatial autocorrelation exhibited by soil C could be extremely valuable for reducing transactions costs associated with contracts for C-credits but the benefits are not uniform across all regions or cropping systems. Accounting for spatial autocorrelation greatly reduced the standard errors and narrowed the confidence intervals associated with sample estimates of the mean number of C-credits produced per hectare. For the payment mechanism considered in this paper, tighter confidence intervals around the mean number of C-credits created per hectare enrolled could increase producer payments by more than 100 percent under a C-contract.
  • Authors:
    • Essah, S. Y. C.
    • Sparks, R. T.
    • Dillon, M. A.
    • Delgado, J. A.
  • Source: Journal of Soil and Water Conservation
  • Volume: 62
  • Issue: 5
  • Year: 2007
  • Summary: This literature review examines a decade of advances in cover crops including how cover crops with limited irrigation can increase yields, crop quality, and nutrient and water use efficiencies while protecting the environment.
  • Authors:
    • Schuman, G. E.
    • Derner, J. D.
  • Source: Journal of Soil and Water Conservation
  • Volume: 62
  • Issue: 2
  • Year: 2007
  • Summary: Management of rangelands can aid in the mitigation of rising atmospheric carbon dioxide concentrations via carbon storage in biomass and soil organic matter, a process termed carbon sequestration. Here we provide a review of current knowledge on the effects of land management practices (grazing, nitrogen inputs, and restoration) and precipitation on carbon sequestration in rangelands. Although there was no statistical relationship between change in soil carbon with longevity of the grazing management practice in native rangelands of the North American Great Plains, the general trend seems to suggest a decrease in carbon sequestration with longevity of the grazing management practice across stocking rates. The relationship of carbon sequestration to mean annual precipitation is negative for both the 0 to 10 cm (0 to 3.9 in) and 0 to 30 cm (0 to 11.8 in) soil depths across stocking rates. The threshold from positive to negative carbon change occurs at approximately 440 mm (17.3 in) of precipitation for the 0 to 10 cm soil depth and at 600 mm (23.6 in) for the 0 to 30 cm soil depth. We acknowledge that largely unexplored is the arena of management-environment interactions needed to increase our understanding of climate-plant-soil-microbial interactions as factors affecting nutrient cycling. Continued refinement of estimates of terrestrial carbon storage in rangelands will assist in the development of greenhouse gas emissions and carbon credit marketing policies, as well as potentially modifying government natural resource conservation programs to emphasize land management practices that increase carbon sequestration.
  • Authors:
    • Gamroth, M.
    • Hart, J.
    • Sullivan, D.
    • Downing, T.
  • Source: Nutrient Management for Dairy Production
  • Year: 2007
  • Authors:
    • McFee, W. W.
    • Kladivko, E. J.
    • Michéli, E.
    • Vyn, T. J.
    • Gál, A.
  • Source: Soil & Tillage Research
  • Volume: 96
  • Issue: 1-2
  • Year: 2007
  • Summary: Numerous investigators of tillage system impacts on soil organic carbon (OC) or total nitrogen (N) have limited their soil sampling to depths either at or just below the deepest tillage treatment in their experiments. This has resulted in an over-emphasis on OC and N changes in the near-surface zones and limited knowledge of crop and tillage system impacts below the maximum depth of soil disturbance by tillage implements. The objective of this study was to assess impacts of long-term (28 years) tillage and crop rotation on OC and N content and depth distribution together with bulk density and pH on a dark-colored Chalmers silty clay loam in Indiana. Soil samples were taken to 1 m depth in six depth increments from moldboard plow and no-till treatments in continuous corn and soybean-corn rotation. Rotation systems had little impact on the measured soil properties; OC content under continuous corn was not superior to the soybean-corn rotation in either no-till or moldboard plow systems. The increase in OC (on a mass per unit area basis) with no-till relative to moldboard plow averaged 23 t ha(-1) to a constant 30 cm sampling depth, but only 10 t ha(-1) to a constant 1.0 m sampling depth. Similarly, the increase in N with no-till was 1.9 t ha(-1) to a constant 30 cm sampling depth, but only 1.4 t ha(-1) to a constant 1.0 m sampling depth. Tillage treatments also had significant effects on soil bulk density and pH. Distribution of OC and N with soil depth differed dramatically under the different tillage systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC and N, relative to no-till, in the 30-50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Our results suggest that conclusions about OC or N gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken well beyond the deepest tillage depth. (c) 2007 Elsevier B.V. All rights reserved.
  • Authors:
    • Robertson, G. P.
    • Grandy, A. S.
  • Source: Ecosystems
  • Volume: 10
  • Issue: 1
  • Year: 2007
  • Summary: Restoring soil C pools by reducing land use intensity is a potentially high impact, rapidly deployable strategy for partially offsetting atmospheric CO2 increases. However, rates of C accumulation and underlying mechanisms have rarely been determined for a range of managed and successional ecosystems on the same soil type. We determined soil organic matter (SOM) fractions with the highest potential for sequestering C in ten ecosystems on the same soil series using both density- and incubation-based fractionation methods. Ecosystems included four annual row-crop systems (conventional, low input, organic and no-till), two perennial cropping systems (alfalfa and poplar), and four native ecosystems (early successional, midsuccessional historically tilled, midsuccessional never-tilled, and late successional forest). Enhanced C storage to 5 cm relative to conventional agriculture ranged from 8.9 g C m(-2) y(-1) in low input row crops to 31.6 g C m(-2) y(-1) in the early successional ecosystem. Carbon sequestration across all ecosystems occurred in aggregate-associated pools larger than 53 mu m. The density-based fractionation scheme identified heavy-fraction C pools (SOM > 1.6 g cm(-3) plus SOM 250 mu m), as having the highest potential C accumulation rates, ranging from 8.79 g C m(-2) y(-1) in low input row crops to 29.22 g C m(-2) y(-1) in the alfalfa ecosystem. Intra-aggregate light fraction pools accumulated C at slower rates, but generally faster than in inter-aggregate LF pools. Incubation-based methods that fractionated soil into active, slow and passive pools showed that C accumulated primarily in slow and resistant pools. However, crushing aggregates in a manner that simulates tillage resulted in a substantial transfer of C from slow pools with field mean residence times of decades to active pools with mean residence times of only weeks. Our results demonstrate that soil C accumulates almost entirely in soil aggregates, mostly in macroaggregates, following reductions in land use intensity. The potentially rapid destruction of macroaggregates following tillage, however, raises concerns about the long-term persistence of these C pools.